The invention relates to an injection pump drive for an engine and more particularly to an improved arrangement for driving the fuel pump of an injection system at varying speeds in response to engine characteristics.
It has been proposed to provide engines with fuel injection systems so as to improve their performance. The use of a fuel injection system is advantageous in that it will insure that the appropriate amount of fuel/air mixture is present in the engine under all running conditions. In addition to applying the use of fuel injection to four cycle engines, fuel injection has been found as a very effective means of controlling the emissions and performance of a two cycle engine.
In conjunction with the use of fuel injection, there is normally provided a high pressure pump for delivering fuel under high pressure to the fuel injector. Normally these pumps are driven from the engine either directly or through some form of gear train. In many engine applications, however, the engine operates at a very wide range of speeds. Therefore, the fuel injection pump itself may be driven at wide speed ranges and with most pumps the output pressure of the pump will vary with the speed at which it is driven. Therefore, it is the normal practice to employ some form of regulating system for regulating the output pressure of the pump so as to maintain a more uniform pressure regardless of the speed variation of the pump. Although the use of regulators is effective, a regulator cannot maintain a full control of the pressure of the fuel pump under all speed conditions since most regulators are effective only to limit the maximum pressure output of the pump. Therefore, it has been the practice to compromise the speed ratio at which the pump is driven and the pressure at which the fuel is regulated so as to achieve optimum performance.
However, the regulation of the pump pressure and the choosing of a single speed ratio for driving the pump is not adequate under all circumstances. For example, during cranking of the engine the engine is normally turned over at a much lower speed than even its normal idle speed. If the pump speed ratio is chosen so that the pump will not output too high a pressure at maximum speed, then the pump output may be somewhat marginal at idle. If this is the case, then during cranking there may be inadequate pump pressure output to supply sufficient fuel to the engine for starting.
It is, therefore, a principal object of this invention to provide an improved fuel pump drive for the injection system of an internal combustion engine.
It is a further object of this invention to provide a fuel pump drive arrangement for a fuel injection system of an engine that operates at varying speed ratios depending upon the engine condition.
It is a further object of this invention to provide a two speed drive for the fuel pump of an engine induction system which will operate the pump at a faster speed ratio during starting than during running.